1. Field of the Invention
The present invention generally relates to a rotary position detecting device designed to convert an angle of rotation of a throttle valve and the like into a corresponding resistance value.
2. Related Art
A Rotary position detecting device used to detect the opening angle of a throttle valve or the like is designed to transmit the movement of an object of detection like a valve shaft or the like and to convert the amount of rotation of a rotor to a corresponding resistance value.
As shown in FIG. 14, for example, a rotary position detecting device 9 disposes a base plate 91 having a resistance circuit surface at the underside thereof and a rotor 92 having contacts 931 and 932 touching the resistance circuit surface in a manner to face each other in a housing 94. The rotor 92 is connected mechanically to the object of detection by certain means and rotated, for example, by means of a lever 941.
As a result, as shown in FIG. 15, first contact 931 slides over resistances 911 and 912 and changes the resistance value between the contacts 951 and 952 depending on the amount of rotation. Second contact 932 short-circuits or opens the connection between conductors 913 and 914 depending on the rotary position of the rotor 92 and thus a specific rotary position can be detected at detection terminals 953 and 954. In FIG. 15, numeral 943 is a coil spring which forces the contacts 931 and 932 against the resistance circuit surface with an appropriate contact pressure (Japanese Utility Model Unexamined Publication No. S62-97909).
Here, in order to accurately detect the rotary position, it is important to precisely adjust the relative position between the resistance circuit surface and the contacts 931 and 932. It should be noted that shaft 921 of the rotor 92 and bearing 942 of the housing 94 are made of metals and main body 922 of the rotor 92, to which the contacts 931 and 932 are attached, is made of an insulating material. In addition, the rotor 92 has the shaft 921 secured to the main body 922 by means of the insert casting or with screws.
The contacts 931 and 932 are, as shown in FIG. 16 and FIG. 17, fixed to the main body 922 of the rotor 92 using a snap washer 934 or the like. The resistance circuit surface is formed on the base plate 91 which is made of an insulating material such as ceramics or resin. On the other hand, the base plate 91 is, as shown in FIG. 14, fixed to a cover 97 via a packing 971. Resistance circuit surface of the base plate 91 is connected to terminals 951 through 954 via a conducting material 96 or the like.
Other than the above-mentioned construction in which the lever 941 fixed to the shaft 921 is rotated by a not-shown valve shaft, it is also known a structure to join the object of detection such as the throttle valve shaft or the like and the rotor 92, in which a fitting hole is provided on the axial center of the shaft 921 to engage or fit the valve shaft. Here, the bottom of the housing 94 is engaged in a recess or the like on the external wall of throttle valve body (Japanese Patent Unexamined Laid-open Publication No. H4-112930). In other words, a tapered protrusion is provided at the bottom of the housing 94 while a recess of the same taper is provided on the valve body side in order to stably install the rotary position detecting device 9 on the throttle valve body.
As another example, the terminal may be, as shown in FIG. 18, constructed in a manner that a conducting member 990 contacting the resistance circuit surface is welded to a terminal 960. The conducting member 990 is made of an elastic material and forces its top section 991 against the resistance circuit surface by the elastic force of recovery which is generated by pressing.
As yet another example of the rotary position detecting device, there is a type of construction in which the resistance circuit surface is formed at the rotor side and the contact is provided on a plate member fixed to the housing (Japanese Patent Unexamined Laid-open Publication No. S62-182449).
However, the rotary position detecting devices according to prior arts have the following problems.
That is, many parts are required to determine the relative position between the resistance circuit surface and the contact and it takes time for the assembly work and adjustment work. Where many parts are used, the relative position between the resistance circuit surface and the contact tends to change and fluctuate depending on the dimensional deviations of respective parts. Cost will also rise as the parts cost as well as the number of assembly work-hours increase.